1. Field of the Invention
The present invention relates to an image forming apparatus which forms an image on a recording material by using an electrophotographic method.
2. Description of the Related Art
An image forming apparatus using an electrophotographic image forming method (electrophotographic process), such as a printer, uniformly charges an electrophotographic photosensitive member (hereinafter, referred to as a “photosensitive member”) serving as an image bearing member and selectively exposes the charged photosensitive member to form an electrostatic image on the photosensitive member. A developing device visualizes the electrostatic image formed on the photosensitive member into a toner image by using a developer (also referred to as toner). The toner image formed on the photosensitive member is transferred to a recording material such as a recording sheet and a plastic sheet. Heat and pressure are further applied to the toner image transferred to the recording material, whereby the toner image is fixed to the recording material. In such a manner, the image forming apparatus performs image recording.
The developing device includes a developer bearing member, a regulating member, and a supply member. For example, the developer bearing member is arranged in an opening of a developer container which stores the toner. The regulating member is arranged in contact with a surface of the developer bearing member, and regulates the amount of toner on the developer bearing member. The supply member rotates in contact with the developer bearing member to supply the toner to the developer bearing member.
Among examples of the developing method is a contact developing method in which the image bearing member and the developer bearing member are in contact with each other when performing development. According to such a method, high quality images can be output with less scattering of toner.
Recently, developing devices of improved image quality to which the electrophotographic process is applied have been needed to handle various media (recording materials). Such developing devices use a unit that makes output at printing speeds optimum for respective media. Suppose that the printing speed (image forming speed) is reduced without changing a circumferential speed ratio between the image bearing member and the developer bearing member. In such a case, fogging has been identified to increase in blank portions as the printing speed decreases. The fogging in blank portions refers to adhesion of toner to the blank portions. Japanese Patent Application Laid-Open No. 2006-171245 discusses that the circumferential speed ratio of the developer bearing member to the image bearing member is made higher in a mode of low printing speed than in a normal mode, whereby the fogging in blank portions is maintained at a near normal mode level.